K2 LiFePO4 batteries

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billvon   1 GW

1 GW
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Joined: Sep 16 2007 9:53pm
Location: san diego

K2 LiFePO4 batteries

Post by billvon » Nov 13 2019 11:28am

I have been seeing these batteries on line - K2 Energy LFP batteries, 25.6V, 9.6AH. They seem to be coming out of some sort of medical equipment, like wheelchairs or something. They are going for very cheap - $50-60 online used. That means $250 per kwhr, which is better than anything outside used EV batteries.

So I got two and ran some tests. Charged to 3.65VPC, discharged to 2.5VPC at about C/2. They clocked in at 7.10 and 7.06 AH respectively. So that means they have about 75% capacity left, and are really about $360/kwhr, which is still not that bad. Still much better than new CALB cells.

I'm considering building a 48V bank out of them for range extension of my current EV (a Prius Prime.) $600 for 2kwhr, which would extend my range by about 9 miles.

FYI.
--bill von

john61ct   100 GW

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Joined: Dec 18 2018 2:06pm

Re: K2 LiFePO4 batteries

Post by john61ct » Nov 13 2019 2:04pm

I have yet to see evidence that K2 makes consistently good quality cells that last anywhere near as long as genuine CALB, GBS, Sinopoly, Winston, A123 et al

even when brand new and proven Grade A from a trusted seller.

I consider 70% SoH to be EoL, most industry uses 80%.

Personally, any secondhand status at all is automatically worth a 40-60% discount from new, even tested higher than 95% SoH, known monitored well-regulated gentle usage and from a trusted seller.

Goes down to 80-90% pretty quickly as those factors are lowered.

But then that's just me, for my use cases longevity is really the most critical factor, my expectation from new is 6-8000 cycles, maybe decades' use, not a quick burnout propulsion style lifetime.

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